Author:

BEEM is a hot-electron (HE) technique based on scanning tunneling microscopy
that can probe buried metal/semiconductor and metal/dielectric interfaces
with nm-scale spatial resolution and energy resolution of a few meV. BEEM is
a three-terminal technique, so the HE energy and interface electric field
can be varied independently. I will discuss two studies of interest for
future transistor technologies. The first concerns the band structure and
alignments in a 20 nm-thick film of the high-k dielectric material
Sc$_{2}$O$_{3}$ grown epitaxially on Si(111). Sc$_{2}$O$_{3}$ and related
rare-earth/transition metal oxide films on Si were found to have similar
band alignments and bandgap, and also ``tailing'' conduction band (CB)
states extending $\sim $1 eV below the primary CB. We combined BEEM with
internal photoemission to measure the band alignment and to study electron
transport through these ``tail'' states.\footnote{W. Cai, S. E. Stone, J. P. Pelz, L. F. Edge, and D. G. Schlom, Appl.
Phys. Lett \textbf{91}, 042901 (2007).} Surprisingly, these tail states
were found to form a robust band of extended states that supports elastic
hot-electron transport even \textit{against} an applied electric field. The second study
concerns HE injection and transport through ``end-on'' metal contacts made
to $\sim $100 nm diameter vertical Si nanowires (NWs) embedded in a
SiO$_{2}$ dielectric. At low HE flux, We observed \textit{lateral variations} of the local Schottky
Barrier Height (SBH) across individual end-on Au Schottky contacts, with the
SBH at the contact edge found to be $\sim $25 meV lower than at the contact
center. Finite-element electrostatic simulations suggest that this is due to
a larger interface electric field at the contact edge due to positively
charged Si/native-oxide interface states near the Au/NW contact, with this
(equilibrium) interface state charge induced by local band bending due to
the high work function Au contact. We also observed a strong \textit{suppression} of the
hot-electron transmission efficiency at larger HE flux, likely due to
(non-equilibrium) \textit{steady-state negative charge accumulation} in metastable traps at the Si/oxide interface located
near the injecting metal contact. Ongoing BEEM measurements of metal
contacts to SrTiO$_{3}$ substrates and films may also be discussed.\\[4pt]
In
collaboration with W. Cai, Y. Che, L. F. Edge, D. G. Schlom, E. R. Hemesath,
and L. J. Lauhon.

*Work supported by NSF Grant No. DMR-0805237

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2012.MAR.T20.2